Fiber reinforced plastic pipe tee

ABSTRACT

A fiber reinforced plastic pipe tee is formed by winding glass rovings around a mandrel in a plurality of wrap patterns which collectively cover the pipe tee. A tape having synthetic fiber warp and glass roving weft is included in wrapping of the pipe tee. Such glass reinforcing fibers are oriented in the tee for resisting biaxial stresses. A bulge is provided on each side of the pipe tee in the diaphragm area for resisting biaxial stresses without introducing problems in winding the pipe tee.

FIELD OF INVENTION

This invention relates to fiber reinforced plastic pipe tees, such as,for example, a glass fiber reinforced epoxy resin tee. A tee geometryand winding patterns are disclosed.

BACKGROUND

Fiber reinforced plastic pipe has come into reasonably extensive use inrecent years for handling corrosive materials, petrochemicals, and thelike where metallic pipe is unsuitable. Glass fiber reinforcements areemployed so that pipe can withstand appreciable pressures. Epoxy resins,commonly with a thin lining resistant to chemicals are often used. Thepipes are formed by winding rovings of glass fiber coated with epoxyresin in helical paths around a cylindrical mandrel and curing theresin. Such pipes can be made economically and it is desirable to makeeconomical fittings for such pipes, such as tees and elbows.

Techniques have been developed for economically winding pipe elbowswhich are essentially sharply curved sections of pipe having two ends.Economical techniques have not been developed for winding pipe teessince they have a much more complicated geometry. Unlike an elbow withtwo ends, a pipe tee has three ends. This greatly complicates thewinding problems since it is important to cover all areas of the teewith a sufficient thickness of fibers with proper orientation forresisting the complex stress distributions in a tee without excessthickness being built up in other areas.

The patterns used for winding the tee must keep the rovings in contactwith or very close to the mandrel on which the tee is wound formaintaining a desired internal geometry in the tee. "Bridging" of fibersacross a concave portion of the tee can result in very low strength inthe bridged areas and require excessive quantities of reinforcement forresisting operating pressures. Commercially available tees are made byhand by laying up a montage of strips of woven fabric. Such assemblytechniques are costly since the woven glass fabric is expensive and alarge amount of hand labor is required. Quality control with suchassembly procedures is also difficult and costly.

There is, therefore, a substantial need for an economical technique forwinding fiber reinforced plastic pipe tees, preferably using relativelyinexpensive glass roving instead of costly woven fabric. Such atechnique must cover all areas of the tee with an adequate thickness ofmaterial to resist the complex stress distribution in a pipe tee withoutexcessive waste or thickness in some areas of the tee.

One area of particular concern because of poor stress distribution isknown as the diaphragm and comprises a roughly triangular area on eachside of the tee near where the three arms of the tee intersect. Thisarea tends to be relatively flat and subject to biaxial stresses whichare large and hard to resist in a non-ductile material such as fiberreinforced plastic.

A variety of configurations have been proposed or used for metal tees,or valve bodies which can be considered to be tees with internal flowcontrol mechanisms. The configuration of the body of a valve is commonlydictated by the internal structure rather than controlled by the stressdistribution. The configuration of metal tees and valves is not aproposto fiber reinforced plastic pipe tees because of the inherent ductilityof the metal as contrasted with brittle behavior of the fiber reinforcedplastic. Because of such ductility stress distributions can be toleratedwhich are unacceptable in a fiber reinforced plastic pipe tee. Suchmetal bodies, of course, have no problems associated with filamentwinding.

A variety of configurations have been proposed for alleviating theadverse stress distributions in the diaphragm area, such as, forexample, making the center portion of the tee as a sphere or ellipse.Such a tee is in the form of a sphere with three arms protruding fromit. Such a pipe tee is described and illustrated in U. S. Pat. No.3,765,979, by Thomas. The pattern of windings provided in that patentcan produce a tee suitable for resisting internal pressure but unsuitedfor a rigid piping system.

The tee in the Thomas patent is suitable for a "blocked" piping systemwhere the pipes and/or fittings are rigidly mounted or "blocked" so thatno appreciable longitudinal loads are transmitted through the jointsbetween pipes and fittings. In such a system an O-ring joint or the likeis used between the end of a piece of pipe and the tee, for example.Such a joint can accommodate limited longitudinal motion, hence imposeslittle, if any, longitudinal stress on the tee. The blocking of thepiping system also minimizes bending loads. In such a system the pipetee is subject to internal pressure stresses and is virtually free oflongitudinal stress and bending.

Since construction of a blocked piping system with rigid mounting iscostly, it is considerably more common to form an integral pipe systemby cementing the pipe fittings, including tees, onto the pipe. In such asystem the pipe tee is essentially a closed end pressure vessel which issubject to longitudinal stress as well as the hoop stresses due tointernal pressure. The pipe tee is also quite likely to be subject tobending stresses due to installation misalignments or changes indimension during operation. A pipe tee suitable for such servicerequires strength in directions not provided by the winding pattern inthe Thomas patent, since that tee is designed for a different type ofservice. Further, since the tee in the Thomas patent has limitedlongitudinal and bending stresses an abrupt transition between thecentral body portion and the three tubular extensions can be acceptable.A different configuration must be provided for a tee employed in asystem having substantial longitudinal and bending stresses both forresisting such stresses and to permit winding filaments in the necessarydirections without bridging of the filaments across recessed regions ofa mandrel. Winding patterns must be developed which cover such a teethoroughly with filaments extending in the principal stress directionswithout use of excessive material and without bridging. It is alsodesirable that the winding patterns be readily implemented in mechanizedwinding equipment so that tees can be made economically and with goodreproducibility.

It is also desirable to develop a configuration for the diaphragm areaof a tee which provides good resistance to biaxial stresses and avoidsproblems in winding the tee.

DEFINITIONS

For purposes of description in this specification, it is convenient toadopt nomenclature representing various portions of a pipe tee such asis provided in practice of this invention. The following glossary ofterms is therefore adopted:

Run: The straight portion of the tee through which fluid can flow in astraight path.

Branch: The cross member of the tee transverse to the run through whichfluid can flow in a right angle path between the branch and run.

Tee Diameter: The nominal diameter of the pipe with which the tee isused; also, the nominal diameter of the run and branch.

Mid-Plane: The plane of symmetry through the tee including the axes ofthe run and branch.

Side: A portion of the tee on one side of the mid-plane.

Back: A portion extending along the run of the tee on the opposite sideof the run from the branch.

Front: A portion of the run facing in the same direction as the branch.

Crotch: Each of the two portions between the branch and an end of therun of the tee, including a portion that is concave in the mid-plane ofthe tee.

Crotch Radius: The radius of curvature of the crotch in the mid-plane ofthe tee.

Diaphragm: A generally triangular area on each side of the body of thetee adjacent the intersection of the run and branch and more or lessparallel to the mid-plane. The size and shape of the diaphragm aredefined to some extent by geometry of the crotch.

Bell: A cylindrical socket at each end of the run and at the end of thebranch, having an inside diameter for receiving the outside of the end(spigot) of a piece of pipe with which the tee is used.

Bell Step: An internal step, generally rounded, between the inner end ofthe bell and the body of the tee which limits the depth of insertion ofa pipe into the bell.

Radial Cross Section: A cross section through the tee normal to themid-plane and formed on two planes, one of which extends radially in onecrotch, and the other of which extends radially in the other crotch orradially across the back of the run.

It is also convenient for purposes of description to define anorthogonal coordinate system for the tee. The X axis is the axis of therun. The Y axis is the axis of the branch. The X-Y plane in this systemis the mid-plane of the tee. The Z axis is normal to the mid-plane andextends through the intersection of the X and Y axes.

BRIEF SUMMARY OF THE INVENTION

Thus, there is provided in practice of this invention, according to apresently preferred embodiment, a fiber reinforced plastic tee formed ofa plurality of different wrap patterns selected from the groupconsisting of:

I--starting at one side of an end of the run, extending helically with afirst hand around the back of the run, through the opposite crotch, thenhelically with a second hand around the back of the run, and ending atthe opposite side of the run at the same end;

II--starting at one side of an end of the run, extending helically witha first hand around the back of the run, then through the oppositecrotch, then circumferentially around the opposite bell and/or bell stepof the run at least one revolution back to the crotch, then helicallywith a second hand around the back of the run, and ending on theopposite side of the same end of the run;

III--starting near the back of the run at one end, extending helicallyaround the run across the diaphragm area, then through the oppositecrotch, then circumferentially around the bell and/or bell step of thebranch at least one-half revolution, then through a crotch, thenhelically around the body of the tee across a diaphragm area, and endingnear the back of the run at an end;

IV--starting at one end of the run extending helically around the runacross a center portion of the back of the run and ending at theopposite end of the run;

V--starting from a crotch, extending helically across one side of thetee and around the back of the run, then across the opposite side of thetee crossing the center plane of the branch near the bell step of thebranch and ending at the end of the branch;

VI--a generally 8-shaped pattern starting in one crotch, extendinghelically with a first hand around the center portion of the back of therun, then through the opposite crotch, then helically with a second handaround the center portion of the back of the run, and ending in thestarting crotch; or a variation starting in one crotch, extendinghelically with a first hand around the center portion of the back of therun, then through the opposite crotch, then an odd number of half turnsaround the branch to the starting crotch, then helically with a secondhand around the center portion of the back of the run, and ending in theopposite crotch; and.

VII--interlacing these wrap patterns.

Preferably an intermediate layer of wraps includes a tape having a warpcomprising several strands of non-reinforcing fiber as a carrier warp,and a weft comprising bundles of substantially straight glass fiberscarried by the carrier strands.

DRAWINGS

These and other features and advantages of the present invention will beappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

FIG. 1 illustrates in side view a destructible mandrel on which a fiberreinforced plastic pipe tee constructed according to principles of thisinvention is wound;

FIG. 2 is a radial cross section through the tee on line 2--2 in FIG. 1;

FIG. 3 is a schematic representation of a wrap pattern for forming thepipe tee;

FIG. 4 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 5 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 6 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 7 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 8 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 9 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 10 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 11 illustrates a variant of the wrap pattern of FIG. 10;

FIG. 12 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 13 is another schematic illustration of another wrap pattern forforming the pipe tee;

FIG. 14 is a view of one face of a glass fiber tape useful for windingpipe tees; and

FIG. 15 is a side view of an exemplary pipe tee constructed according toprinciples of this invention.

DESCRIPTION

A fiber reinforced plastic pipe tee is formed by winding fiberreinforcements on an expendable mandrel having an external configurationcorresponding to the internal shape of the tee being formed. Reinforcingfibers coated with epoxy resin or the like are wound on the mandreluntil a sufficient thickness of material has been built up in all areasto withstand the stresses imposed on the pipe tee. The resin is cured,such as by heating, and excess material at the ends of the tee istrimmed off. The frangible or soluble mandrel on which the tee is woundis shattered or dissolved. If desired a protective film can be appliedto the mandrel before winding to become part of the tee and protect theplastic from materials carried in the tee.

Such an internal mandrel is illustrated in side view in FIG. 1 and in anapproximation of a representative radial cross section in FIG. 2. Thedefinitions set forth above for the tee are applicable to the mandrel.Thus, the mandrel has a straight run 11 and a side branch 12perpendicular to the axis of the run. At each end of the run and branchthere is an enlarged bell 13. The diameter of the bell corresponds tothe outside diameter of the end or "spigot" of a pipe with which the teeis used, allowing for clearance for adhesive used in assembling the pipeand tee. That is, the bell on the mandrel has an outside diametercorresponding to the inside diameter in the bell of the tee within whichthe pipe can be inserted. Regardless of the presence of the bells, therun and branch can each be considered to be in the general form of aright circular cylinder.

A phantom line 14 is shown on each bell 13 indicating the place wherethe tee is trimmed. When the tee is wound on the mandrel some of thewinding material builds up on the end portions of the mandrel beyond thetrim lines 14. It is desirable to minimize the quantity of materialbeyond the trim lines for minimizing waste.

A bell step 16 is provided inboard of each bell 13 extending between thelarger diameter of the bell and the smaller diameter of the tee. Thenominal tee diameter, that is, the diameter of the run and branch, isthe nominal diameter of pipe with which the tee is used. The bell steplimits the distance the end of a pipe can be inserted into the bell.

A crotch 17 is formed between the branch 12 and each end of the run 11.

A generally triangular diaphragm area 18 is defined on each side of thetee where the run and branch intersect. Assuming that a tee were madewith a cylindrical branch intersecting a cylindrical run with no radiusin the crotch there would be a line intersection and the diaphragm areawould be nil. As the radius of the crotch increases, the size of thediaphragm area also increases and the centroid of the diaphragm areashifts towards the end of the branch.

Absent special measures such as provided on the mandrel herein describedand illustrated, the diaphragm area would be flat and subject to highstresses. A symmetrical bulge is therefore formed on the mandrelcentered on the centroid of the diaphragm area. The bulge blendssmoothly into all portions of the branch and run and into both crotchestherebetween. The bulge is large enough to alleviate the adverse stressdistribution if the diaphragm area were flat and is small enough that itdoes not introduce bridging or other problems during winding ofreinforcing fibers on the tee. A smooth transition between the bulge andadjacent portions of the tee is important not only for stressdistribution but also for winding filaments without bridging.

The surface of each crotch 17 includes a portion in the form of a partof a torus. The minor radius of the torus (i.e., the radius of thecircular generatrix) is the same as the radius of the run. The center 19of the torus is equidistant from the axis 21 of the run (Y axis) and theaxis 22 of the branch (X axis) in the mid-plane of the tee and locatedso that the center 23 of the generatrix of the torus is tangent to theseaxes as near the inner end of the bell step 16 as possible. The center23 of the generatrix of the torus in each crotch is illustrated as adashed line in FIG. 1. The major radius of the torus is the distancefrom the center 19 to the center 23 of the circular generatrix of thetorus. This gives the largest possible crotch radius within the lengthlimits of a standard size tee. It also assures smooth blending of thecrotch into the run and branch. The crotch radius (i.e., the radius ofthe curvature of the crotch in the mid-plane of the tee) is thedifference between the major and minor radii of the torus.

It is convenient to define a "directrix" for determining the geometry ofthe bulge in the diaphragm area. As used herein, the directrix is thelocus of points in the mid-plane of the tee that is equidistant from thecenter 23 of the generatrix of the torus forming one crotch and either(a) the axis of the run, or (b) from the center of the generatrix of thetorus forming the other crotch. Two of the three legs of the directrixare illustrated in FIG. 1 as a dotted line 24 extending from a point oftangency with the axis 21 near each end of the run to an intersectionwith the axis 22 of the branch. The third leg of the directrix thenextends along the axis of the branch. The intersection of the directrix24 with the axis 22 of the branch is regarded as the centroid of thediaphragm. A circle (not shown) centered on the centroid and having aradius equal to the distance from the centroid to the axis of the run istangent to the center 23 of the generatrix of each of the toruses.

FIG. 2 is an arbitrarily selected representative radial cross sectionthrough Point A taken on line 2--2 in FIG. 1. This cross section extendsas a radial plane through the torus of one crotch to the intersectionwith the directrix and then in a radial plane through the back of therun. Point A is the intersection of the radial cross section with thedirectrix at a location with coordinates X and Y. Point B is on the axisof the run. Point C is on the center of the generatrix of the torus.Points B and C are equidistant from Point A because of the definition ofthe directrix.

As pointed out in greater detail hereinafter, the radial cross sectionillustrated in FIG. 2 is an approximation of the actual radial crosssection of a mandrel formed in accordance with the techniques described.This cross section is useful for exposition of the geometry of the bulgeformed on each side of the tee and the technique for forming such abulge. Because of practical machining considerations, the bulge differsslightly from the mathematical approximation and an indication of theactual radial cross section obtained is included as a dashed line 36 inFIG. 2.

Such a radial cross section is bilaterally symmetrical on opposite sidesof the directrix regardless of the arbitrarily selected location ofPoint A. It can be noted that this is also true for a radial crosssection taken through a "Point A" located on the axis of the branch.Such a cross section extends along radial planes through each of the twotoruses in the respective crotches. It can also be noted that if "PointA" is the centroid of the diaphragm there is three-way symmetry; thatis, on a radial plane through each torus and on a radial plane throughthe run.

The diaphragm is a roughly triangular area on each side of the body ofthe tee subject to substantial stress when the tee is pressurized. Thediaphragm area 18 outlined in FIG. 1 is a projection of the axis 21 ofthe run and the center 23 of the generatrix of the torus in each crotch.A flat area having this shape would be present on a tee made with eachcrotch in the form of a simple torus and with the branch and run each inthe form of a right circular cylinder. FIG. 2 includes a phantom line 26along each side indicating the shape of a diaphragm at Section 2--2 ifthe tee were made with a cylindrical run, a cylindrical branch, and asimple torus in each crotch, that is, without the bulges on each side.Such a diaphragm has a large flat area, at a distance from the mid-planecorresponding to the radius of the run and has high stresses because ofthe flat area subjected to internal pressures within the tee. Such aflat area is to be avoided when a pipe tee is made with material such asglass fiber reinforced epoxy that has little, if any, ductility.

As mentioned above, a symmetrical "bulge" is formed on each side of thetee centered over the centroid of the diaphragm area 18. The bulgeblends smoothly into the torus in each crotch and into the cylindricalsurface of the run. Bilateral symmetry in each radial cross sectionthrough the directrix as hereinabove described is maintained. It shouldbe noted that the back of the run opposite the branch is straight; thatis, the back of the run remains substantially as a cylinder and thebulge does not extend around the back. Extending the bulge around theback of the run does not increase the strength in that region and can bea detriment in resisting longitudinal stress. It can increase the amountof material needed without concomitant benefit.

The geometry of the bulge can be expressed in mathematical terms as twonumbers, R and Z. This can be understood by considering the machiningemployed for forming a mold in which the mandrel illustrated in FIGS. 1and 2 is cast. Such machining can be done with a ball mill or fly cutterhaving a spherical radius R. The center of the ball mill is placed at aposition above the directrix defined by X and Y coordinates such as inthe Z direction above Point A. The ball mill is plunged into the mold soas to cut beyond the plane of the diaphragm area illustrated in FIG. 1to form a spherical depression in the mold, hence, a spherical bulge onthe mandrel. The number Z is the coordinate of the center of thespherical mill above the mid-plane of the tee at the full depth of thecut.

A plurality of such spherical indentations are formed in the mold withthe center of the ball mill traversing a series of X and Y coordinatesalong each leg of the directrix. The radius R of the sphere and thedepth of plunge in the Z direction beyond the plane of the diaphragm aredetermined mathematically for the X and Y coordinates at selectedlocations on the directrix.

To make an absolutely smooth surface on the bulge and transition to thecylinder and toruses an infinite number of such machining cuts would berequired along the directrix. In a practial pipe tee this is notrequired and fewer than a score of such machining cuts can be employedwith half a dozen sizes of ball mills. The slight irregularitiesremaining can be sanded away by hand to form an essentially smoothsurface having nearly the desired geometry. For example, the bulge on athree inch tee can be made with one cut at the centroid and half a dozencuts along each leg of the directrix, leaving less than 1/32 inch handsmoothing.

It should be noted that the representative radial cross section shown insolid lines in FIG. 2 does not actually exist except at the centroid ofthe diaphragm when a mold is made with a machining technique using aspherical mill or the like as described. This is due to the intersectionof the sphere of the mill with the cylindrical projection of the run orbranch in locations beside the representative cross section. Forexample, a spherical mill can also remove material from the mold at alocation along the run nearer the end of the run than the center of thesphere. This is a consequence of the radius R of the sphere being largerthan the nominal radius of the run (or branch).

Generally speaking, the largest radius sphere is employed opposite thecentroid of the diaphragm. The sphere becomes progressively smalleralong each leg of the directrix approaching the radius of the run (orbranch) at the end of each leg. The larger radius ball mill removes somematerial from a region to be machined by an adjacent smaller radius ballmill. The consequent deepening of the recess machined in the mold iscentered along the directrix. Thus, the bulge on the mandrel cast inthat mold is somewhat further from the mid-plane than projected solelyon the basis of the representative cross section illustrated in FIG. 2.In effect, the representative cross section is only a two-dimensionalconsideration and the actual machining operations occur in threedimensions. A dashed line 36 is included in one sector of the crosssection in FIG. 2 indicating an approximation of the actual crosssection obtained by a machining technique as herein described. Thedashed line represents a surface having a series of circular arcs formedby successive ball mills and blended together by hand smoothing, the arcnearest the centroid representing a larger ball mill and the arcsfurther from the centroid representing progressively smaller ball mills.

The representative radial cross section illustrated in solid lines inFIG. 2 is useful for defining the radius of the ball mill and the X, Yand Z coordinates of each machining cut to provide smooth blending ofthe bulge into the run and branch cylinders, and the torus in eachcrotch.

The radius R of the ball mill and the Z coordinate of the center of thespherical mill above the mid-plane of the tee at the full depth of theplunging cut can be determined by four equations. Two of these equations

are employed when the X coordinate is greater than zero, that is, the Ycoordinate is less than the distance between the centroid of thediaphragm area and the axis of the run. This corresponds to the twodotted line portions of the directrix 24 illustrated in FIG. 2. A secondset of equations is employed for determining R and Z when X equals zero,that is, as Y increases along the portion of the directrix along theaxis 22 of the branch beyond the centroid.

When X is different from zero, the Y coordinate for each X coordinatealong the directrix is found by the equation Y=(b-x)² /4b, where b isthe major radius of the torus. At the centroid of the diaphragm the Ycoordinate is b/4.

When X is different from zero and Y is less than b/4, the Z coordinateand spherical radius R are determined by the equations: ##EQU1## When Xequals zero and Y is equal to or greater than b/4, the coordinate Z andradius R are determined by the equations: ##EQU2## In these equations ais the radius of the run (and also the minor radius of the torus) and bis the major radius of the torus. The angle θ is in the range of from25° to 75° and preferably is 40° to 50°.

The angle θ can be understood by reference to FIG. 2 which is anarbitrary radial cross section through the tee as hereinabove described.For the bulge to blend smoothly into the surface of the run or crotch,the circular cross section of the bulge should intersect the circularcross section of the run (for example) where the radii of both circlesare coincident; that is, where tangents to the two circles arecoincident. For each cross section of the type illustrated in FIG. 2there are four points where the circles of the bulge and the run orcrotch are tangent as indicated by Point D. A line from such a point oftangency through Point B (the axis of the run), for example, intersectsa line perpendicular to the directrix at the angle θ at Point E whichhas the coordinate Z determined by one of the equations set forthhereinabove. To make a cut in a mold for casting the mandrel, a millwith spherical radius R is plunged into the mold until the center of theradius on the mill is at Point E, that is, it has a coordinate Z abovethe mid-plane.

The choice of angle θ is determined in part by the radius of the crotch.A smaller angle θ is appropriate when the radius is large and a largerangle θ is preferred when the crotch radius is small. This is a functionnot of the absolute radius of the crotch but of the radius relative tothe radius of the run. The preferred angle θ can be considered as afunction of the major and minor axes of the torus forming each crotch.

The size of the torus that can be accommodated in the crotch of a tee isconstrained by the standard sizes of fittings that have been adopted byindustry. For example, the total length of a tee of a given diameter hasbeen specified so that the designer of a piping system can fix thedimensions of the system without regard to the source of the fittings.Because of such constraints, the torus in a two inch tee has a ratio ofb/a (major radius over minor radius) of about 1.9. On a twelve inch teethe b/a ratio is about 1.54. Intermediate sizes have intermediateratios. For example, a nominal four inch tee has a b/a ratio of about1.75.

When the b/a ratio is as low as 1.5, the angle θ is preferably in therange of from about 35° to 75° and most preferably is about 50°. Whenthe b/a ratio is about 1.9, the angle θ is chosen in the range of fromabout 25° to 55° and most preferably is about 40°. When the b/a ratio isabout 1.75, the angle θ is chosen in the range of from about 30° to 65°and preferably about 45°. When the b/a ratio is between 1.5 and 1.9, theangle θ is in a range that is an interpolation between the ranges setforth above.

If the angle θ is less than the lower number for the various ratiosmentioned above, the diaphragm area on the tee is so nearly flat thatthere is insufficient benefit in stress distribution so that an excessof winding material can be required for obtaining appropriate strengthin the diaphragm area. Extra material is needed in the diaphragm areafor resisting the pressure and longitudinal stresses and in addition anexcess of material can be built up in the adjacent areas as additionalwindings are applied. In particular, an excess of material canaccumulate on the back of the run due to the winding patterns used tocover the diaphragm area. Such use of excess material can contributesignificantly to the cost of the tee since the materials are expensive.

If the angle θ is more than the larger numbers mentioned above forvarious b/a ratios, an excessively large bulge is formed on the sides ofthe tee, leading to difficulties in winding reinforcing fibers onto thetee. Difficulties can arise due to bridging in the vicinity of the bellstep on the branch when there is a large bulge on the side of the tee.Further, an excess of material can accumulate in the center of the backof the run. The large bulge can also be undesirable for optimum flowcharacteristics through the tee.

Preferably, the angle θ is about 40° to 50° since this gives optimumcurvature for strengthening the diaphragm area without leading towinding problems in a fiber reinforced plastic pipe tee.

FIG. 2 is a cross section through a tee where the angle θ is chosen as45°. If the angle θ were 30° for example, the intersection of the bulgewith the run would be further from the mid-plane of the tee. Point Ewould be much further to the left in FIG. 2 (Z would be larger) and thediaphragm region would be more nearly flat, i.e., closer to the phantomline 26 in FIG. 2. If the angle θ were 65°, the bulge would be muchlarger and the radial cross sections more nearly circular.

In the exemplary embodiment the angle θ is chosen as 45° throughout thetraverse along the directrix. As another approximation of an ellipticalbulge, the angle θ selected for each cut can progressively change foreach position along the directrix, tending to be smaller near thecentroid and gradually increasing toward the end of the directrix.

Each radial cross section through the bulge could be made in the form ofa mathematical ellipse and have complete bilateral symmetry across the Zaxis. This is not necessary for a practical fiber reinforced plasticpipe tee and a psuedo-ellipitcal cross section which is a closeapproximation of an ellipse is quite satisfactory. Eachpseudo-elliptical radial cross section is centered on the directrix. Inthe bulge the largest difference between the major axis and the minoraxis of the cross sections is greatest through the centroid of thediaphragm. The difference decreases smoothly towards zero in planesthrough the center 19 of each torus and normal to the axis of either therun or branch. Thus, the cross section reduces to a circle where thecenter of the generatrix of the torus is tangent to the respective axisadjacent the bell step. Because at each radial cross section the bulgeis tangent to the cylindrical run and the torus of the crotch, thetransitions at the edges of the bulge are smooth.

A most significant selection of the angle θ and hence, the radius R ofthe sphere, is at the centroid of the diaphragm. This selectiondetermines the principal dimensions of the bulge on each side of thetee. The balance of the values of R and θ along each leg of thedirectrix help define a smooth transition between the central portion ofthe bulge and the surfaces of the run, branch and torus in each crotch.The value selected for the angle θ at locations along each leg of thedirectrix can therefore differ from the values set forth above aspreferred for the center of the bulge without significantly changing theeffect of the bulge. It is convenient, however, to select the same angleθ throughout the length of each leg of the directrix.

Preferably, the maximum height of the bulge above the mid-plane of thetee, i.e., above the centroid of the diaphragm, is in the range of from(a+0.06b) to (a+0.16b). Preferably, the height of the bulge at itscentroid is in the range of (a+0.09b) to (a+0.12b). Stated otherwise,the height of the bulge above the diaphragm plane 26 (which is at radiusa) is in the range of from 6 to 16% of the major radius of the torus andis preferably about 9 to 12% of the major radius of the torus. If theheight of the bulge is less than about 6% an excess of material must bebuilt up in the diaphragm area to resist stresses. If the height is morethan about 16% problems can be introduced in winding fibers on the tee.A maximum height of the bulge at its centroid of about 9 to 12% of themajor radius of the torus provides a good balance between stressdistribution and ability to wind the fiber reinforced tee withoutbridging or other difficulties.

To facilitate winding strands of reinforcing fiber for forming a pipetee, each end of the mandrel has structure beyond the trim line 14. Acircumferential flange 27 at the end of each bell 13 keepscircumferential windings placed around the bell from slipping off theend during winding. A smaller diameter drum or post 28 is provided ateach end of the run. These drums provide locations from which wrappatterns can commence. Flanges 29 on outer ends of the drums also helpretain reinforcing fibers in position. A boss 31 is also provided ateach end of the run for supporting the mandrel. A generally cylindricalnose 32 is provided beyond the flange 27 on the branch.

A pipe tee is preferably wound using glass roving. A roving is a bundleof small diameter substantially parallel glass fibers. Several suchrovings can be wound in parallel in the form of a band two centimetersor more in width. Such rovings can be immersed in a liquid epoxy resin,for example, before winding, for forming a dense layer of plasticreinforced by glass fibers on the mandrel.

Another material particularly useful for winding a pipe tee is referredto herein as a tape. It is not the usual woven strip employed in handlay-up of pipe tees where both the warp and weft are glass fibers. Asillustrated in FIG. 14 the preferred tape has several synthetic warpstrands 41, such as nylon, serving as a carrier web for short parallelbundles 42 of straight glass fibers as a weft. The carrier fibers havevery little strength as compared with the glass and hence are notreinforcing fibers in the completed tee. Such a tape is commerciallyavailable and has been used with polyester resin for forming boat hulls,for example.

A typical tape suitable for winding a pipe tee has about a dozen warpstrands of nylon spaced apart across the width of the tape forsupporting the weft. The weft is formed of bundles of parallel glassfibers about 6 centimeters long. The bundles are made of short glassfibers ending at the end of the bundle as distinguished from a wovenfabric in which the weft strands are continuous fibers repeatedlydoubled back on themselves at a selvage. A typical bundle is about 3millimeters wide and a small fraction of a millimeter thick. The warpstrands are knitted into a series of interlocking loops with each looploosely holding a bundle of glass fibers. This leaves the bundlessomewhat spaced apart along the length of the tape, the space betweenadjacent bundles being in the order of 1.5 to 2 millimeters. Otherdimensions of such tapes are useful.

Such a tape is particularly useful for forming a pipe tee since theloosely knitted synthetic warp strands can stretch and slip laterallyfor curving the tape without bunching or deforming the bundles of glassfibers. The loose looping also permits skewing; that is, when the tapeis wound on a mandrel the bundles of glass fibers need not remainperpendicular to the warp strands, although the bundles of glass fibersremain essentially parallel to each other. This is significant so thatthe tape can lie against the curved surfaces of the tee, particularly inthe crotch region, and the bundles of glass fibers can be maintained inalignments that are parallel to the principal directions of stress,thereby forming a strong pipe tee with minimal use of material. Such atape is preferred over woven fabric because of such properties.

An exemplary pipe tee constructed according to principles of thisinvention is illustrated in a side view in FIG. 15. Such a tee is formedby winding resin coated glass fiber rovings 44 or tape (not shown inFIG. 15) onto a mandrel such as illustrated in FIG. 1 until a sufficientthickness is built up to obtain the desired strength. The resin is curedand the mandrel removed. The ends of the tee are trimmed (e.g., alonglines 14 in FIG. 1) to remove excess material. The exterior of the teeconforms generally to the mandrel with a straight run 45 and a lateralbranch 46. Each end has a bell 47 having an inside surface correspondingto the bell surface 13 on the mandrel. Some of the precise geometry ofthe inside of the tee is lost on the exterior due to the inherentroughness of the body produced by the winding process.

To form a pipe tee by winding a mandrel with resin coated fibers aplurality of different wrap patterns are employed. Each wrap is capableof covering a portion of the mandrel and collectively the wraps cancover the entire mandrel for forming a tee having adequate strengththroughout. There is no single wrap that can cover the entire tee and acombination of patterns is needed. These patterns can be described bythe path of a roving or tape extending from an end of the tee along apath on the body and off an end of the tee, or a path commencing at alocation on the body of the tee and extending along the body of the teeeither to an end or to a location on the body. Such an end can be ateither end of the run or the end of the branch.

For convenience in this description these patterns are lettered by lowercase letters enclosed in parentheses. Basic patterns are describedcommencing, for example, at one location such as an end of the run. Itwill be understood that mirror images of such patterns, such ascommencing at the opposite end of the run, are included.

Eight basic patterns useful for wrapping a pipe tee are illustrated inFIGS. 3 to 10. These drawings are schematic and ignore the enlarged belland bell step, the bulge on the side of the tee and the drums and noseat the ends of the tee. Such details have been deleted to avoidobscuring the winding patterns. Since the illustrations are schematicthey are not necessarily accurate projections. These patterns arerepresentative and variations are employed covering adjacent areas onthe tee so that the entire tee area can be covered.

Each pattern is illustrated by a line extending around the tee. Such aline can be thought of as a roving wrapped on the tee. When the line ison the exposed portion of the tee, it is continuous with superimposedarrowheads indicating direction for purposes of understanding. When theline is on the hidden portion of the tee it is in effect a dashed lineand only arrowheads are illustrated.

These wrap patterns are described as having a first hand of helix or asecond hand of helix. A particular pattern may be illustrated as aright-handed helix, however, it will be understood that a mirror imageof the pattern can be a left-handed helix. Similarly, such a pattern cancommence at an opposite end of the tee or on the opposite side of themid-plane to thoroughly cover the tee.

Basic patterns include the following:

(a) starting at one side of an end of the run, extending helically witha first hand around the back of the run, through the opposite crotch,then helically with a second hand around the back of the run, and endingat the opposite side of the run at the same end, as illustrated in FIG.3;

(b) starting at one side of an end of the run, extending helically witha first hand around the back of the run, then through the oppositecrotch, then circumferentially around the opposite bell step of the runat least one revolution back to the crotch, then helically with a secondhand around the back of the run, and ending on the opposite side of thesame end of the run, as illustrated in FIG. 4;

(c) starting on one side of the tee near the back of the run at one end,extending helically with a first hand around the run across thediaphragm area, then through the opposite crotch, then circumferentiallyaround the bell step of the branch at least one-half revolution, thenthrough the nearer crotch, then helically with a second hand around thebody of the tee across the same diaphragm area, and ending on one sideof the tee near the back of the run at the opposite end, as illustratedin FIG. 5;

(d) starting near the back of the run at one end extending helicallywith one hand around the run across the diaphragm area, then through theopposite crotch, then circumferentially around the bell of the branch atleast one-half revolution, then through the nearer crotch, thenhelically with a second hand around the body of the tee across the samediaphragm area and ending near the back of the run at the opposite end,as illustrated in FIG. 6;

(e) starting on one side at an end of the run, extending helically witha first hand around the back and the opposite side of the run, thenthrough the opposite crotch, then circumferentially around the belland/or bell step at the opposite end of the run, then through theopposite crotch and helically with a second hand across the startingside of the run and circumferentially around the bell and/or bell stepat the starting end of the run, then through the nearer crotch, thenhelically with the first hand around the back of the run, and ending onthe starting side of the tee at the opposite end of the run, asillustrated in FIG. 7;

(f) starting at one end of the run, extending helically around the runacross a center portion of the back of the run and ending at theopposite end of the run, as illustrated in FIG. 8;

(g) starting from a crotch, extending helically across one side of thetee and around the back of the run, then across the opposite side of thetee crossing the center plane of the branch (Y-Z plane) near the bellstep of the branch and ending at the end of the branch, as illustratedin FIG. 9;

(h) a generally 8-shaped pattern starting in one crotch, extendinghelically with a first hand around the center portion of the back of therun, then through the opposite crotch, then helically with a second handaround the center portion of the back of the run, and ending in thestarting crotch, as illustrated in FIG. 10; or a variation starting inone crotch, extending helically with a first hand around the back of therun, then through the opposite crotch, then an odd number of half turnsaround the branch to the starting crotch, then helically with a secondhand around the back of the run and ending in the opposite crotch (asillustrated in FIG. 11).

If desired, before commencing such windings the surface of the mandrelcan be covered with a film that bonds to the plastic and protects theplastic of the tee from corrosive contents when the tee is put inservice.

To make the windings on the mandrel for forming a pipe tee, one end of aroving is connected to a drum 28 at an end of the tee. Masking tape orthe like followed by a few circumferential turns around the drumprovides a sufficiently secure attachment. The winding is then carriedover the flange 27 on to the bell at the end of the run at a selectedlocation and helix angle for commencing one of the patterns.

The preferred helix angle along the cylindrical portion of the run orbranch is about 54° for resisting both the internal pressure and thelongitudinal stress due to use of the tee in a system applying stressesanalogous to a closed end pressure vessel. The helix angle is the anglebetween the helical path and the axis of the run, for example. In theregion of the diaphragm it is preferred that the windings tend to beorthogonal to each other, hence, the helix angle tends to approach 45°relative to the axis of the run. The average helix angle on the tee istypically less than the optimum 54°. Average helix angle on a specificpipe tee depends in part on the total length of the tee. For example, anominal two inch tee has a length of about five diameters while a teesix inches or larger has a total length of only about three diameters.On a relatively long tee the helix angle can change along the length ofthe run and more closely approach the optimum 54° at the end of the bellthan in a shorter tee.

The helix angle referred to is for windings traversing the surfacediagonally. It will be recognized that parts of several winding patternsare only slightly diagonal or could be considered to have a helix angleof almost 90°. When such a winding is made with a tape, the reinforcingfibers have a helix angle approaching 0°. When longitudinally extendingand circumferentially extending fibers are present due to such windingsit is desirable to have about 100% greater strength in thecircumferential direction due to a larger number of fibers than in thelongitudinal direction. This provides a structure having strengthapproximately the strength of a structure in which all windings are atabout 54°.

Not all of the helical paths on the run of the tee are at the averagehelix angle. Typically, the helix angles are within a range of plus orminus 10° from the average helix angle so that the helical paths cancover all portions of the tee and still fit tightly against the surfaceswithout slippage parallel to the surface of the mandrel. Some change inthe helix angle can occur along the length of the helix as the effectivediameter of the helix changes on different portions of the tee. Thus,for example, the helix angle may be different as a winding crosses thebulge in the diaphragm area as compared with the helix angle of the samehelical path adjacent the bell step.

An example of change in helix angle in different portions of a windingis illustrated in Pattern (d). In this pattern the wrap extends towardsthe end of the branch as a left-handed helix as illustrated in FIG. 6.The helix angle gradually increases as the wrap approaches the end ofthe branch until it reaches 90° whereupon it becomes a right-handedhelix and continues away from the end of the branch with graduallydecreasing helix angle. Such a pattern is employed near an end of thetee for reversing direction without going off the end of the tee withconsequent waste of material beyond the trim lines. It is significantthat the rate of change of the helix angle be small enough that slippageof the roving parallel to the surface of the tee is avoided.

In addition to assuring coverage of the entire tee, it can also besignificant to change the helix angle in the various wrap patterns sothat each area on the tee has reinforcing fibers extending in aplurality of directions essentially parallel to the surface forresisting biaxial stresses. Preferably fibers are provided diagonallywith respect to the axis of, for example, the run of the tee.

A helix angle of concern is the angle as the winding crosses the flange27 at an end of the mandrel. The diameter of the drum 28 at each end ofthe run is proportioned in accordance with the average helix angle asthe windings cross the flange. The ratio of the diameter of the drum tothe diameter of the flange at the end of the bell is the sine of thehelix angle. With this proportion a winding can cross the flange withoutcircumferential or longitudinal slippage. Deviations by individualwindings of plus or minus 10° from the average helix angle are readilyaccommodated without slippage due to friction which tends to hold thewindings in position on the mandrel.

Pattern (g) which extends off the end of the branch employs the nose 32for turning. Thus, a roving extends off the branch at a low helix angle,makes a half turn around the nose and returns over the end of the branchat a location spaced apart from where it went off the branch so that thetwo paths can cross in the region of the bell step. The ratio of thediameter of the nose 32 to the diameter of the flange 27 on the branchis the sine of the average helix angle of the windings in Pattern (g).

Each winding pattern illustrated in FIGS. 3 to 10 provides coverage of aselected region of the tee. Coverage of the bell step at one end of thetee is exemplary. Pattern (a) crosses the bell step in a diagonaldirection near the back of the run. Pattern (b) crosses the bell stepdiagonally on a side of the tee more or less midway between the frontand the back. Pattern (f) crosses the bell step diagonally near thefront of the tee. These patterns can be applied as right-handed and thenleft-handed helixes. Collectively, these patterns provide diagonallyextending fibers across substantially the entire circumference of thebell step.

Pattern (b) also includes at least one circumferential winding aroundthe bell step providing circumferentially extending fibers. A pluralityof diagonal or helical windings of Patterns (a), (b), and (f) can bemade across the bell step, followed by a circumferential winding aroundthe bell step. The diagonal windings have a tendency to bridge acrossthe bell step. The circumferential windings compensate for such tendencyby forcing the diagonal windings towards the mandrel in the region ofthe bell step. The region of the bell step can be partly filled withcircumferential windings before Patterns (a), (b), and (f) are appliedso that outer layers of diagonal windings have less tendency to bridge.

Diagonal fibers cross the back of the run at the mid-plane by reason ofseveral of the patterns. Pattern (d) provides diagonal fibers at the endof the run. The next region towards the center is covered by Pattern (c)followed by Patterns (a), (b), and (f). Pattern (e) also providesdiagonal fibers in a region along the back more or less overlappingregions covered by Patterns (b) and (f). These patterns also build updiagonally extending fibers over the bells at the ends of the run andover much of the sides of the run.

Diagonally extending fibers are laid across the diaphragm by Patterns(a), (c), and (d) and in the outer portions of the diaphragm along therun by Pattern (b).

An area of some difficulty is in the region of the bell step on eachside of the branch. This area is covered by Pattern (g) which alsoprovides nearly circumferentially extending fibers across the back ofthe run. Circumferential fibers around the bell on the branch areprovided by Pattern (d) and to some extent Pattern (c). Circumferentialfibers around the bells at the ends of the run are provided by Pattern(e). It should be noted that circumferential windings around the bellscan be provided as an extension of any of the patterns having acircumferential turn adjacent he bell. Thus, for example, Pattern (b)can be extended to provide circumferential fibers around the bells atthe end of the runs.

Diagonal fibers are provided by winding rovings through the crotch atdifferent angles. Pattern (b) applies diagonal fibers in the portion ofthe crotch near the run. Pattern (a) applies fibers nearer the middle ofthe crotch. Pattern (c) applies diagonal fibers in the portion of thecrotch nearer the branch. Pattern (e) applies fibers near the middle ofthe crotch at one end and nearer the run at the opposite end. Patterns(c), (d), and (g) provide diagonal fibers on the branch.

As described herein, many of the patterns commence at an end of the run,for example, and terminate at an end of the run. Since a combination ofpatterns is employed in winding a pipe tee, strict adherence to apattern as described and illustrated in FIGS. 3 to 10 is not essential.Thus, a shift from one pattern to another can be made on the body of thetee. For example, a shift can be made between patterns as the windingproceeds through a crotch or in a circumferential path around a bell.These switches are more readily made than switches in the course of ahelical winding since, with notable exception of Pattern (e), the helixangles generally tend to carry the winding off an end of the tee.Patterns (g) and (h) are exemplary of switches. Each of these patternscommences at a location in a crotch and can be easily interleaved withinanother pattern that extends through a crotch or circumferentiallyaround a bell at the end of the run.

Such interleaving is not illustrated herein for clarity in the drawingsand since a very large number of cross overs from one pattern to anotherare feasible. Such cross overs between patterns on the mandrel inboardof the trim lines are desirable for minimizing waste of materialoutboard of the trim lines.

Exemplary of a cross over or switch of patterns is the variation inPattern (h) mentioned above. In effect, this is a switch from one-halfof an 8-shaped pattern commencing with a first hand to half of another8-shaped pattern having an opposite hand. This cross over isparticularly advantageous for interleaving of adjacent windings on bothsides of the tee and building up material in the bell step of the branchwithout extending the windings beyond the trim lines.

Relations will be apparent among the patterns of windings illustrated inFIGS. 3 to 10. Thus, Patterns (c) and (d) are similar except that theycross the branch at different distances from the run. Pattern (b)resembles half of Pattern (e), differing in the helix angle such that awinding in Pattern (b) terminates at an end of the run whereas it couldcontinue through a crotch and, in effect, become half of a Pattern (e).

Variations in the patterns are also apparent. For example, Pattern (c)is described and illustrated as having a one-half turn (or odd number ofone-half turns) around the branch so that the winding crosses itself inthe diaphragm area on one side of the tee. Such a winding could take aneven number of one-half turns around the branch and cross the diaphragmarea on the opposite side of the tee.

The variations in Pattern (h) mentioned above are also exemplary. Inwinding a tee it can be desirable to employ such variations for coveringthe entire surface with fibers oriented in appropriate directions. Forexample, the first variant of Pattern (h) can be employed for placingtape in the portion of the crotches adjacent the run and the secondvariant can be employed for placing tape in the portion of the crotchesnearer the branch.

Precession of the patterns at different starting locations and differenthelix angles is employed for covering all areas of the body of a tee.Pattern (f) is exemplary. One winding of Pattern (f) may start at thefront of the tee on one side, cross the mid-plane on the front of thebell, cross the back of the run nearer the opposite end and terminate atthe opposite end of the tee on the opposite side relatively near theback. The next winding in Pattern (f) may start at the front of the teeat about the mid-plane, cross the back of the run near the middle andproceed to termination at the opposite end appreciably closer to thefront of the tee than the termination of the first winding. Successivewindings can commence nearer and nearer the back of the tee and endnearer the front of the tee. The helix angles between successivewindings can change so that the windings effectively fan from the backof the run; that is, adjacent windings are relatively closer together atthe back of the run and relatively further apart on the bell. Similarvariations of each of the other patterns can be employed.

The sequence of patterns for covering the surface of the tee isgenerally not important, except for minimizing the quantity of windingmaterial built up beyond the trim lines 14. Thus, as many shifts betweenpatterns is made on the tee as feasible to minimize the number of timesthe winding goes off an end. Further, the patterns are preferablysequenced so that substantially less than a full turn is made around adrum between the end of one pattern and the commencement of the next. Itis desirable to change patterns or the hand of patterns frequentlyrather than build up substantial thickness with one pattern. Crossingfibers are desirable in thin layers since this increases interlaminarshear area as compared with fewer, thicker layers. A stronger part canbe made with the same quantity of material.

One can, for example, commence with a few repetitions of Pattern (a)starting at a series of locations at one end of the tee. Patterns (c),(d) and (f) can then be added for providing diagonal reinforcing fibersaround substantially the entire circumference of one of the bell steps.Patterns (c), (d), and (f) each commence at one end of the run andterminate at the opposite end of the run. Thus, at a convenient point inthis sequence additional repetitions of Pattern (a) can be added at theopposite end of the run. Patterns (c), (d) and (f) can also be employedfor changing the hand of the helix at each end of the run. A pluralityof repetitions of Pattern (b) can then be superimposed for addingcircumferential windings in the bell steps to overcome any briding ofthe diagonal windings. Suitable repetitions of Patterns (c), (d) and/or(f) can be interleaved with Pattern (b) for changing hand and ends ofthe tee. Such variations and repetitions are continued for interleavingadditional patterns on the tee.

A first layer of windings can be built up on the mandrel, employing acombination of variations of Patterns (a) through (g). This effectivelycovers the entire mandrel with rovings of glass fiber coated with epoxy.Most areas are covered with diagonally extending fibers.

A second layer is then formed employing a tape as hereinabove described.This intermediate layer contains reinforcing fibers that extendtransverse to reinforcing fibers in the first layer by reason of thestructure of the tape employed. An important aspect of this layer is inthe region of the two crotches. The crotches are subject to hoopstresses which are resisted by essentially radially and diagonallyextending fibers in windings extending through the crotches in the firstlayer. They are also subject to a more or less longitudinally extendingstress that is not effectively resisted by the fibers which go throughthe crotch at a large angle to the mid-plane of the tee. There is astress in the mid-plane, for example, that tends to pull the run andbranch away from each other, or enlarge the angle between the branch andrun.

It is therefore desirable to wind a tape through the crotch regionsaccording to Pattern (h). The tape extends through the crotch in anapproximately radial plane. This provides reinforcing fibers extendingin the desired direction in the crotch; that is, parallel or nearlyparallel to the mid-plane. The variation in Pattern (h) placesreinforcing fibers on the branch parallel to its axis.

Circumferential windings of the tape around the bells and the back ofthe run provide longitudinal reinforcement. This is particularlysignificant in the region of the bell on the branch. Only limitedapplication of diagonally extending fibers can be provided on the belland bell step by glass rovings without excessive waste as the windingsextend beyond the trim lines. The tape applies glass fibers extendinglongitudinally along the bell and bell step and blending into adjacentparts of the crotch. Circumferential windings of rovings resist hoopstresses. Thus, strength can be built into the branch with somewhatlower efficiency than in areas where diagonal fibers are more readilyapplied.

Windings of the tape extending diagonally across the diaphragm providesignificant reinforcement in that region, as well. In the diaphragm area(i.e., over the bulges) and on some portions of the run the glass fiberbundles forming the weft of the tape tend to skew relative to thewinding direction so that they are not normal to the warp. Surprisingly,when such a tape is wound diagonally across the diaphragm area andthrough a crotch, the weft is skewed so that the reinforcing fibers tendto align themselves with the axis of the branch. This is a direction ofweakness and such alignment of the reinforcing fibers is advantageous.

Helix angles of the wraps and the number of wraps of tape in eachpattern are selected for building up a desired thickness of reinforcingfibers in each direction in each portion of the tee. This can beaccomplished in the intermediate layer using Patterns (a) through (e)and (h).

Coating of such a tape with epoxy or other resin is not convenient. Itis therefore desirable to also wind a band of glass fiber rovings on themandrel coincident with the winding of the tape. The glass fiber rovingsare passed through a bath of liquid resin before winding and serve as acarrier for liquid resin for impregnating the tape. This co-winding oftape and roving is also advantageous since it interleaves layers withtransverse fibers, significantly increasing interlaminar shear area andstrength of the tee.

After the intermediate layer formed of tape and rovings of the desiredthickness has been built up over the inner layer on the mandrel, a thirdor outer layer is built up in a manner similar to the inner layer, usingglass fiber rovings. Patterns (a) through (g) are employed for coveringthe entire area of the tee.

In the embodiments described the inner and outer layers are built upwith rovings sandwiching the layer containing tape. This tends to assurea smooth surface on the tee and contain the bundles of glass fibers inthe intermediate layer, ends of which might otherwise protrude from thetee. This is particularly significant in some regions where the tapecrosses convex portions of the tee and the more or less straight bundlesof glass fibers would otherwise extend away from the surface.

There are also advantages to forming a tee using co-windings of rovingsand tape for most of the thickness of the tee commencing at the insidesurface adjacent the mandrel. In such an embodiment the innermost layerincludes the tape and only the outermost layer, which can be relativelythin, comprises only glass rovings for assuring a smooth surface on theexterior of the tee. Protrusion of the ends of fibers from the inside ofthe tee is not of concern since the resin is cured before removal of themandrel. This type of winding can be desirable for providing increasedinterlaminar shear area adjacent the inside surface of the tee.

The tee can be wound by rotating the mandrel and feeding roving and/ortape from a movable source or the roving and/or tape can be fed fromrotatable spools moved around the mandrel, or a combination of suchmotions can be used. After the tee is wound using a combination ofwinding patterns as hereinabove described, the liquid resin issolidified such as by heating or curing at room temperature. The mandrelis then removed from the tee, either before or after trimming the endsof the run and branch.

The winding patterns employed in the exemplary pipe tee hereinabovedescribed utilize both rovings and the special tape that can deform tofit tightly against surfaces with compound curvature. It can bedesirable to construct a pipe tee wound from only rovings. Such a pipetee involves more waste of material in end trimming than does anembodiment employing the hereinabove described tape. Economic trade offscan be made between end losses, cost increment of tape versus rovings,and the complexity of the winding patterns for each embodiment of pipetee for selecting a preferred technique for winding a tee.

An area of some difficulty in an embodiment wound entirely with rovingslies in each crotch and particularly in the portion of the crotch in themid-plane of the tee extending towards the end of the branch. In thisregion it is difficult to build up reinforcing fibers extendinglongitudinally along the branch. Additional winding patterns can beemployed for building up material in this region.

One such pattern is illustrated in FIG. 12 and is identified as Pattern(i). This winding pattern commences at the end of the branch more orless in the vicinity of the mid-plane of the tee. The winding thenextends helically along the branch with a small helix angle, across thediaphragm area on one side of the tee, around the back of the run, andhelically across the opposite side of the tee to the opposite crotch.After passing through the crotch, the winding extends helically alongthe branch with a large helix angle to the end of the branch. In theschematic illustration of FIG. 12, the end point of this winding patternat the end of the branch is about 90° counterclockwise from the startingpoint. This angle is appropriate for the schematic illustration butsubject to appreciable variation due to differences in the length of thebranch in various sizes of tees. Several such windings can be built upon the mandrel with the starting and ending points shifting clockwiseand/or counterclockwise around the end of the branch to cover anextended area on the tee.

Pattern (i) has an interesting feature at the end of the branch. When aroving extends off the end of the branch as illustrated in FIG. 12, itthen makes a partial turn around the nose 32 (FIG. 1) at the end of thebranch on the mandrel. The roving can then come off the end of thebranch on the opposite side of the tee in a repetition of Pattern (i),that is a mirror image of the pattern illustrated in FIG. 12. Thisbuilds up fibers in both crotches and on both sides of the tee in alogical and symmetrical sequence.

Another pattern suitable for winding a pipe tee with rovings, referredto herein as Pattern (j), is illustrated in FIG. 13. Two segments ofsuch a pattern are illustrated in the drawing.

Pattern (j) commences at an end of the run on one side of the tee,extends in a helical path around the run through the nearer crotch, thenhelically around the branch to the end of the branch on the oppositeside of the tee from the starting point. A return path of Pattern (j)starts at an end of the branch on the opposite side of the tee from theend of a preceding path, extends helically around the branch through thesame crotch, then helically around the run to the end of the run on theopposite side from the start of a preceding path. When a pair of suchwinding patterns are started from similar points on opposite sides ofthe tee they cross in the mid-plane of the tee in the crotch. Bystarting and ending at differing locations around the ends of the runand branch, the locus of crossing can be varied along the mid-planethrough the crotch and along the branch.

It is desirable to use Pattern (j) since this pattern provides fiberswith a substantial longitudinally extending component in the crotch nearthe mid-plane of the tee. Other patterns can be used to provide suchlongitudinally extending fibers but a plurality of such patterns can beneeded for adequately covering all portions of the crotch. ThesePatterns (i) and (j) place rovings with a substantial longitudinalcomponent high in the crotch, that is, nearer the end of the branch.Rovings having a substantial component extending longitudinally alongthe run and lying lower in the crotch can be provided by Patterns (b) or(f), for example. If desired, Patterns (i) and (j) can be used in anembodiment employing both tape and rovings for winding a tee. It ispreferred, however, to delete these patterns since each contributesheavily to waste of material upon end trimming and somewhat similarlyoriented fibers can be readily applied by use of the above-describedtape.

A preferred combination of winding patterns for forming a pipe tee usingentirely rovings comprises at a minimum Patterns (c), (f), (i) and (j).Collectively, these patterns can be employed for providing reinforcingfibers with suitable orientations on all portions of the pipe tee. It isdesirable, however, in such an embodiment to also include Patterns (a)and (b). This is desirable since some of the regions on the tee are moreeasily covered than with other windings, particularly in certain typesof automatic winding machinery.

Another combination of patterns suitable for forming a pipe tee madesolely with windings of rovings requires Patterns (f), (h) and (i), plussubstantially circumferential windings around the bell step and bell ateach end of the run and branch. Desirable patterns to include in such acombination are Patterns (a), (b) and (c). Patterns (b) and (c) caninclude a plurality of substantially circumferential windings around theends of the run and branch.

Still another combination of patterns suitable for forming a pipe teeusing only rovings requires Patterns (b), (c), and (i). In such anembodiment the starting point of Pattern (b) is moved around the end ofthe run so that in some wraps there is a large helix angle for coveringall portions of the pipe tee with fibers having appropriate orientationsfor carrying the applied stresses. In order to minimize this requirementit is preferred to also include Pattern (f) in the windings. Additionalpatterns that can be included to make winding such a tee easier arePatterns (a) and (h) and circumferential windings around the bell andbell step at each end of the run and branch, particularly around thebranch since Patterns (b) and (c) can include a plurality ofcircumferential windings around the ends of the run and branch.

It will be noted that Pattern (i) is important in each embodiment ofpipe tee formed by winding only rovings. Shifting of Pattern (i) amongvarious starting and stopping points at the end of the branch can easilycover much of the crotch and diaphragm areas with fibers suitablyoriented for resisting applied stresses. Further, Pattern (i) is readilyimplemented on a machine for automatically winding pipe tees. Although apipe tee can be wound with all rovings without using Pattern (i), suchan embodiment requires substitution of several different patterns toassure coverage of all areas on the pipe tee.

Although described in limited embodiments, many modifications andvariations will be apparent to one skilled in the art. Thus, forexample, the embodiments have been described in the context of epoxyresin and glass fibers. Other fibers and synthetic plastic materialssuch as polyester resin can clearly be substituted. The pipe tee isdescribed with a bell for receiving the spigot of a pipe. Alternatively,the tee can be formed without a bell or bell step, that is, with the runand branch extending essentially as a cylinder. Such an embodiment isused, for example, by machining the exterior of the ends of the run andbranch for receiving a flange which is cemented in place, therebyproducing a fiber reinforced plastic pipe tee for flange connections.Many other modifications and variations will be apparent to thoseskilled in the art and it is therefore to be understood that within thescope of the appended claims this invention can be practiced otherwisethan as specifically described.

What is claimed is:
 1. A fiber reinforced plastic pipe tee having astraight run and a side branch comprising:a plurality of laminations ofessentially continuous reinforcing fiber roving bonded together by asynthetic resin, including at least some layers of tape having a weft ofparallel reinforcing fibers and a warp of carrier fibers for maintainingthe reinforcing fibers substantially parallel to each other, thereinforcing fibers having ends embedded beneath fiber rovings adjacentthe outside surface of the tee.
 2. A pipe tee as recited in claim 1wherein a portion of such tape is wrapped through each crotch betweenthe branch and run with the length of the tape extending in anapproximately radial plane.
 3. A pipe tee as recited in claim 1 whereinat least a portion of such tape is wrapped in a generally 8-shapedpattern extending through each crotch between the branch and run andcrossing on the back of the run opposite the branch.
 4. A pipe tee asrecited in claim 1 wherein a portion of the reinforcing fibers of theweft of the tape are parallel to the mid-plane of the tee in the area ofeach crotch between the branch and run.
 5. A pipe tee as recited inclaim 1 wherein at least a portion of such tape is wrappedcircumferentially around each end of the tee.
 6. A pipe tee as recitedin claim 3 wherein at least a portion of such tape is wrapped in apattern extending from one crotch between the run and branch around theback of the run, through an odd number of one half turns around thebranch to the starting crotch, and around the back of the run to theopposite crotch.
 7. A pipe tee as recited in claim 1 wherein at least aportion of the reinforcing fibers in the weft of such tape adjacent suchan end of the tee are parallel to the axis of the end of the tee.
 8. Apipe tee as recited in claim 1 wherein at least a portion of thereinforcing fibers in the weft of the tape are parallel to the axis ofthe run along at least a portion of the length of the back of the runopposite the branch.
 9. A pipe tee as recited in claim 1 wherein atleast a portion of the reinforcing fibers in the weft of the tape in thediaphragm area on each side of the tee near the intersection of the runand branch lie approximately parallel to the axis of the branch.
 10. Afiber reinforced plastic pipe tee having a straight run and a sidebranch comprising:a laminated structural layer comprising a plurality ofwraps of tape having a weft of reinforcing fibers and a warp ofnon-reinforcing carrier fibers, the reinforcing fibers having endsembedded in the layer, the layer being bonded by synthetic resin; and anouter laminated layer comprising a plurality of wraps of reinforcingfiber roving bonded with a synthetic resin.
 11. A pipe tee as recited inclaim 10 wherein the structural layer further comprises a plurality ofwraps of reinforcing fiber roving interleaved with the tape.
 12. A pipetee as recited in claim 10 wherein a portion of such tape is wrappedthrough each crotch between the branch and run with the length of thetape extending in an approximately radial plane.
 13. A pipe tee asrecited in claim 10 wherein at least a portion of such tape is wrappedin an 8-shaped pattern extending through each crotch between the branchand run and crossing on the back of the run opposite the branch.
 14. Apipe tee as recited in claim 10 wherein a portion of the reinforcingfibers of the weft of the tape are parallel to the mid-plane of the teein the area of each crotch between the branch and run.
 15. A pipe tee asrecited in claim 10 wherein at least a portion of such tape is wrappedcircumferentially around each end of the tee.
 16. A pipe tee as recitedin claim 13 wherein at least a portion of such tape is wrapped in apattern extending from one crotch between the run and branch around theback of the run, through an odd number of one half turns around thebranch to the starting crotch and around the back of the run to theopposite crotch.
 17. A pipe tee as recited in claim 10 wherein at leasta portion of the reinforcing fibers in the weft of such tape adjacentsuch an end of the tee are parallel to the axis of the end of the tee.18. A pipe tee as recited in claim 10 wherein at least a portion of thereinforcing fibers in the weft of the tape are parallel to the axis ofthe run along at least a portion of the length of the back of the runopposite the branch.
 19. A pipe tee as recited in claim 10 wherein atleast a portion of the reinforcing fibers in the weft of the tape in thediaphragm area on each side of the tee near the intersection of the runand branch lie approximately parallel to the axis of the branch.
 20. Apipe tee as recited in claim 10 further comprising an inner laminatedlayer comprising a plurality of wraps of reinforcing fiber roving bondedwith a synthetic resin inside the structural layer.
 21. A fiberreinforced plastic pipe tee having a straight run and a side branch, apair of crotches between the branch and run and a diaphragm area on eachside of the mid-plane of the tee near the intersection of the branch andrun, comprising a plurality of wraps of reinforcing fiber rovings havingthe oattern (V) starting from a crotch, extending helically across oneside of the tee and around the back of the run, then across the oppositeside of the tee crossing the center plane of the branch and ending atthe end of the branch; and further comprising a sufficient plurality ofdifferent optional wraps of reinforcing fiber rovings for covering theentire pipe tee selected from the groups of patterns consisting of:(I)starting at one side of an end of the run, extending helically with afirst hand around the back of the run, through the oppoiste crotch, thenhelically with a second hand around the back of the run, and ending atthe opposite side of the run at the same end; (II) starting at one sideof an end of the run, extending helically with a first hand around theback of the run, then through the opposite crotch, thencircumferentially around the opposite end of the run at least onerevolution back to the crotch, then helically with a second hand aroundthe back of the run, and ending on the opposite side of the same end ofthe run; (III) starting near the back of the run at one end, extendinghelically around the run across the diaphragm area, then through theopposite crotch, then circumferentially around the branch at least onehalf revolution, then through a crotch, then helically around the bodyof the tee across a diaphragm area, and ending near the back of the runat an opposite end; (IV) starting at one end of the run extendinghelically around the run across a center portion of the back of the runand ending at the opposite end of the run; (VI) a generally 8-shapedpattern starting in one crotch, extending helically with a first handaround the back of the run, then through the opposite crotch, thenhelically with a second hand around the back of the run, and ending inthe starting crotch; (VII) starting in one crotch, extending helicallywith a first hand around the back of the run, then through the oppositecrotch, then at least one half turn around the branch to the startingcrotch, then helically with a second hand around the back of the run andending in the opposite crotch; and (VIII) interleavings of saidpatterns.
 22. A pipe tee as recited in claim 21 comprising:an innerlayer comprising Patterns (I) through (V); an intermediate layercomprising Patterns (I), (II), and (III), and Pattern (VI) or (VII); andan outer layer comprising Patterns (I) through (V).
 23. A pipe tee asrecited in claim 22 wherein the intermediate layer comprises at least aportion of glass fibers in bundles having ends within the intermediatelayer.
 24. A pipe tee as recited in claim 21 further including a patternstarting on one side at an end of the run, extending helically with afirst hand around the back and the opposite side of the run, thenthrough the opposite crotch, then circumferentially around the oppositeend of the run, then through the opposite crotch and helically with thesecond hand across the starting side of the run and circumferentiallyaround the starting end of the run, then through the nearer crotch, thenhelically with the first hand around the back of the run, and ending atthe opposite end of the run.
 25. A fiber reinforced plastic pipe teehaving a straight run and a side branch, a pair of crotches between thebranch and run and a diaphragm area on each side of the mid-plane of thetee near the intersection of the branch and run comprising a pluralityof wraps containing reinforcing fiber roving including at least somewraps of each of the following patterns:(I) starting at one side of anend of the run extending helically with a first hand around the back ofthe run, through the opposite crotch, then helically with a second handaround the back of the run, and ending at the opposite side of the runat the same end; (II) starting at one side of an end of the run,extending helically with a first hand around the back of the run, thenthrough the opposite crotch, then circumferentially around the oppositeend of the run at least one revolution back to the crotch, thenhelically with a second hand around the back of the run, and ending onthe opposite side of the same end of the run; (III) starting near theback of the run at one end, extending helically around the run acrossthe diaphragm area, then through the opposite crotch, thencircumferentially around the branch at least one-half revolution, thenthrough a crotch, then helically around the body of the tee across adiaphragm area, and ending near the back of the run at an end; (IV)starting at one end of the run extending helically around the run acrossa center portion of the back of the run and ending at the opposite endof the run; (V) starting from a crotch, extending helically across oneside of the tee and around the back of the run, then across the oppositeside of the tee crossing the center plane of the branch and ending atthe end of the branch; and (VI) a generally 8-shaped pattern starting inone crotch, extending helically with a first hand around the back of therun, the through the opposite crotch, then helically with a second handaround the back of the run, and ending in the starting crotch; or (VII)starting in one crotch, extending helically with a first hand around theback of the run, then through the opposite crotch, then at leastone-half turn around the branck to the starting crotch, then helicallywith a second hand around the back of the run and ending in the oppositecrotch.
 26. A pipe tee as recited in claim 25 further including apattern starting on one side at an end of the run, extending helicallywith a first hand around the back and the oppoiste side of the run, thenthrough the opposite crotch, then circumferentially around the oppositeend of the run, then through the opposite crotch and helically with thesecond hand across the starting side of the run and circumferentiallyaround the starting end of the run, then through the nearer crotch, thenhelically with the first hand around the back of the run, and ending atthe opposite end of the run.
 27. A pipe tee as recited in claim 25comprising:an inner layer comprising Patterns (I) through (V); anintermediate layer comprising Patterns (I), (II), (III) and (VI) or(VII); and an outer layer comprising Patterns (I) through (V).
 28. Apipe tee as recited in claim 27 wherein the intermediate layer comprisesat least a portion of glass fibers in bundles having ends within theintermediate layer.
 29. A fiber reinforced plastic pipe tee having astraight run and a side branch, a pair of crotches between the branchand run and a diaphragm area on each side of the mid-plane of the teenear the intersection of the branch and run comprising a plurality ofdifferent wrap patterns of reinforcing fiber roving including at leastsome wraps of each pattern from the group consisting essentially of:(I)starting at one side of an end of the run, extending helically with afirst hand around the back of the run, through the opposite crotch, thenhelically with a second hand around the back of the run, and ending atthe opposite side of the run at the same end; (II) starting at one sideof an end of the run, extending helically with a first hand around theback of the run, then through the opposite crotch, thencircumferentially around the end of the run at least one revolution backto the crotch, then helically with a second hand around the back of therun, and ending on the opposite side of the same end of the run; (III)starting on one side of the tee near the back of the run at one end,extending helically with a first hand around the run across thediaphragm area, then through the opposite crotch, then circumferentiallyaround the branch a plurality of one-half revolutions relatively nearerthe intersection of the run and branch, then through the nearer crotch,then helically with a second hand around the body of the tee across thesame diaphragm area, and ending near the back of the run at the oppositeend; (IV) starting near the back of the run at one end extendinghelically with one hand arounddthe run across the diaphragm area, thenthrough the opposite crotch, then circumferentially around the branchone-half revolution relatively nearer the end of the branch than pattern(III), then through the nearer crotch, then helically with a second hsndaround the body of the tee across the same diaphragm area and endingnear the back of the run at the opposite end; (V) starting on one sideat an end of the run extending helically with a first hand around theback and the opposite side of the run, then through the opposite crotch,then circumferentially around the opposite end of the run, then throughthe opposite crotch and helically with the second hand across thestarting side of the run and circumferentially around the starting endof the run, then through the nearer crotch, then helically with thefirst hand around the back of the run, and ending at the opposite end ofthe run; (VI) starting at one end of the run extending helically aroundthe run across a center portion of the back of the run and ending at theopposite end of the run; (VII) starting from a crotch, extendinghelically across one side of the tee and around the back of the run,then across the opposite side of the tee crossing the center plane ofthe branch and ending at the end of the branch; and (VIII) a generally8-shaped pattern starting in one crotch, extending helically with afirst hand around the back of the run, then through the opposite crotch,then helically with a second hand around the back of the run, and endingin the starting crotch; or (IX) starting in one crotch, extendinghelically with a first hand around the back of the run, then through theopposite crotch, then at least one-half turn around the branch to thestarting crotch , then helically with a second hand around the back ofthe run and ending in the opposite crotch.
 30. A pipe tee as recited inclaim: 28 further comprising at least some layers of tape having a weftof parallel reinforcing fibers having ends embedded beneath fiberrovings in other layers and a warp of non-reinforcing carrier fibers.31. A fiber reinforced plastic pipe tee having a straight run and a sidebranch comprising a plurality of laminations of reinforcing fibersbonded together by synthetic resin including at least some layers oftape having a weft comprising a plurality of bundles of parallelreinforcing fibers and a carrier warp sufficiently loosely holding thebundles to permit skewing of the bundles relative to the length of thetape before curing the resin and at least some layers of essentiallycontinuous reinforcing fiber rovings.
 32. A pipe tee as recited in claim31 wherein such layers of rovings are interleaved between such layers oftape.
 33. A pipe tee as recited in claim 31 wherein the reinforcingfibers in the bundles have ends embedded beneath the outside surface ofthe tee.
 34. A pipe tee as recited in claim 33 including an outermostlayer consisting essentially of such essentially continuous reinforcingfiber rovings.
 35. A pipe tee as recited in claim 31 wherein a portionof such tape is wrapped through each crotch between the branch and runwith the length of the tape extending in an approximately radial plane.36. A pipe tee as recited in claim 31 wherein at least a portion of suchtape is wrapped in a generally 8-shaped pattern extending through eachcrotch between the branch and run and crossing on the back of the runopposite the branch.
 37. A pipe tee as recited in claim 31 wherein aportion of the reinforcing fibers of the weft of the tape are parallelto the mid-plane of the tee in the area of each crotch between thebranch and run.
 38. A pipe tee as recited in claim 36, wherein at leasta portion of such tape is wrapped in a pattern extending from one crotchbetween the run and branch around the back of the run, through an oddnumber of one-half turns around the branch to the starting crotch, andaround the back of the run to the opposite crotch.
 39. A pipe tee asrecited in claim 31 wherein at least a portion of the reinforcing fibersin the weft of such tape adjacent such an end of the tee are parallel tothe axis of the end of the tee.
 40. A pipe tee as recited in claim 31wherein at least a portion of the reinforcing fibers in the weft of thetape are parallel to the axis of the run along at least a portion of thelength of the back of the run opposite the branch.
 41. A pipe tee asrecited in claim 31 wherein at least a portion of the reinforcing fibersin the weft of the tape in the diaphragm area on each side of the teenear the intersection of the run and branch lie approximately parallelto the axis of the branch.
 42. A fiber reinforced plastic pipe teehaving a straight run and a side branch comprising a plurality of layersof reinforcing fibers bonded together by synthetic resin comprisinginterleaving of a first plurality of layers of essentially continuousreinforcing fiber rovings and a second plurality of layers of bundles ofparallel reinforcing fibers having ends embedded beneath the outsidesurface of the tee and extending transverse to such rovings.
 43. A pipetee as recited in claim 42 including an outermost layer consistingessentially of such essentially continuous reinforcing fiber rovings.44. A pipe tee as recited in claim 42 wherein at least a portion of thebundles are parallel to the mid-plane of the tee in the area of eachcrotch between the branch and run.
 45. A pipe tee as recited in claim 42wherein at least a portion of the bundles adjacent an end of the tee areparallel to the axis of the end of the tee.
 46. A pipe tee as recited inclaim 42 wherein at least a portion of the bundles are parallel to theaxis of the run along at least a portion of the length of the back ofthe run opposite the branch.
 47. A pipe tee as recited in claim 42wherein at least a portion of the bundles in the diaphragm area on eachside of the tee near the intersection of the run and branch lieapproximately parallel to the axis of the branch.
 48. A fiber reinforcedplastic pipe tee having a straight run and a side branch, a pair ofcrotches between the branch and run and a diaphragm area on each side ofthe mid-plane of the tee near the intersection of the branch and run,comprising at least some wraps of reinforcing fiber rovings from each ofthe group of patterns consisting of:(I) starting near the back of therun at one end, extending helically around the run across the diaphragmarea, then through the opposite crotch, then circumferentially aroundthe branch at least one half revolution, then through a crotch, thenhelically around the body of the tee across a diaphragm area, and endingnear the back of the run at an opposite end; (II) starting at one end ofthe run extending helically around the run across a center portion ofthe back of the run and ending at the opposite end of the run; (III)starting at the end of the branch, extending helically with a first handat a relatively smaller helix angle along the branch, across thediaphragm area, then around the back of the run, then helically with asecond hand across the opposite side of the run, then through the crotchopposite from the region of the start, then helically with the firsthand at a relatively larger helix angle along the branch on the sameside of the tee as the diaphragm area and ending at the end of thebranch; and (IV) starting at an end of the run, extending helically witha first hand along the run, then through the nearer crotch, then alongthe branch with the same hand, and ending at the end of the branch. 49.A pipe tee as recited in claim 48 further comprising at least some wrapsfrom the following patterns:(V) starting at one side of an end of therun extending helically with a first hand around the back of the run,through the opposite crotch, then helically with a second hand aroundthe back of the run, and ending at the opposite side of the run at thesame end; and (VI) starting at one side of an end of the run, extendinghelically with a first hand around the back of the run, then through theopposite crotch, then circumferentially around the opposite end of therun at least one revolution back to the crotch, then helically with asecond hand around the back of the run, and ending on the opposite sideof the same end of the run.
 50. A fiber reinforced plastic pipe teehaving a straight run and a side branch, a pair of crotches between thebranch and run and a diaphragm area on each side of the mid-plane of thetee near the intersection of the branch and run, comprising at leastsome wraps of reinforcing fiber rovings from each of the group ofpatterns consisting of:(I) starting at one side of an end of the run,extending helically with a first hand around the back of the run, thenthrough the opposite crotch, then circumferentially around the oppositeend of the run at least one revolution back to the crotch, thenhelically with a second hand around the back of the run, and ending onthe opposite side of the same end of the run; (II) starting near theback of the run at one end, extending helically around the run acrossthe diaphragm area, then through the opposite crotch, thencircumferentially around the branch at least one half revolution, thenthrough a crotch, then helically around the body of the tee across adiaphragm area, and ending near the back of the run at an opposite end;(III) starting at the end of the branch, extending helically with afirst hand at a relatively smaller helix angle along the branch, acrossthe diaphragm area, then around the back of the run, then helically witha second hand across the opposite side of the run, then through thecrotch opposite from the region of the start, then helically with thefirst hand at a relatively larger helix angle along the branch on thesame side of the tee as the diaphragm area and ending at the end of thebranch; and (IV) starting at one end of the run extending helicallyaround the run across a center portion of the back of the run and endingat the opposite end of the run.
 51. A pipe tee as recited in claim 50further comprising at least some wraps from the patterns comprising:(V)starting at one side of an end of the run, extending helically with afirst hand around the back of the run, through the opposite crotch, thenhelically with a second hand around the back of the run, and ending atthe opposite side of the run at the same end; and (VI) a generally8-shaped pattern starting in one crotch, extending helically with afirst hand around the back of the run, then through the opposite crotch,then helically with a second hand around the back of the run, and endingin the starting crotch; or (VII) starting in one crotch, extendinghelically with a first hand around the back of the run, then through theopposite crotch, then at least one half turn around the branch to thestarting crotch, then helically with a second hand around the back ofthe run and ending in the opposite crotch.
 52. A pipe tee as recited inclaim 51 further comprising a plurality of substantiallycircumferentially extending wraps around each end of the run and branch.53. A pipe tee as recited in claim 50 further comprising a plurality ofsubstantially circumferentially extending wraps around each end of therun and branch.